This invention relates to semiconductor circuits, and more particularly, relates to providing a switchable injector current source for those semiconductor circuits known as integrated injection logic (I.sup.2 L) circuits.
I.sup.2 L circuits offer high packing density, low power dissipation, and relatively good speed. For reasons of cost and reliability, attempts are being made to accommodate a maximum number of circuit components on a single chip. Not only does I.sup.2 L offer the high packing density but it also offers relatively low cost processing. Some of the items that consume a considerable amount of semiconductor area on a chip are the diffused resistors which require a very great area, components which must be isolated from other components on the same chip, and metal lines which are used to interconnect the different components on the chip. When isolating partial circuits from each other the isolation must extend through the whole expitaxial layer down to the substrate. In addition, to the isolation diffusion width tolerance problems caused by the special masking step detrimentally affect the packing densities obtainable. Moreover the diffusion operation entails additional time and process requirements and leads to reduced yields in many cases. It is therefore preferable to group several circuit components within one isolation pocket. It will therefore be appreciated that it would be desirable to utilize circuitry that is compatible with the high packing density of I.sup.2 approaches and yet uses a minimum number of metal lines to interconnect the different circuits.
Accordingly it is an object of this invention to provide a switchable injector current source which is compatible with the high density approach of I.sup.2 L technology.
Another object of this invention is to provide a switchable injector current source which permits a relatively reduced die size because of the reduction of metal line routing.
Yet another object of the present invention is to provide a switchable injector current source which can drive several nodes from a single line.